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Sr12

(Sheen and Snyder, 1964) (Plate 3-15)

Sr12 was first used in conjunction with Sr11 to designate complementary genes thought to be present in Gabo, Lee and Timstein (Knott and Anderson, 1956). Luig (1960) and Sears and Loegering (1961) showed that a single gene (Sr11) was involved and that abnormal gametic transmission rates were responsible for the disturbed genetic ratios originally observed by Knott and Anderson (1956). Sheen and Snyder (1964) then used Sr12 to designate a gene in a Thatcher derivative.

Chromosome Location

Low Infection Type

;, 2, X to 3.

Environmental Variability

Most effective at temperatures below 20°C.

Origin

Sr12 is derived from T. turgidum var. durum cv. Iumillo and was transferred to Marquillo and, eventually, Thatcher as part of the transference of rust resistance from Iumillo to bread wheat (Hayes et al., 1920).

Pathogenic Variability

Virulence is reported to be common. However, RA McIntosh believes this gene is more effective than reported in the literature. Sr12 also shows interactions with other genes, especially the Sr9 alleles, Sr9b and Sr9g.

Source Stocks

Australia: Tincurrin; Windebri. Celebration Sr9g Sr16 (RA McIntosh, unpublished 1980). Tentative results based on multi-pathotype surveys in Australia indicate that Sr12 may be relatively common. Unfortunately, Sr12 is often difficult to distinguish from Sr6 with Australian P. graminis pathotypes and appropriate genetic studies have not been pursued.

Seedling leaves of (L to R): Thatcher, Celebration, Lee, Condor, CS/Marquis 3B and Chinese Spring; infected with A. pt. 34-2, 4, 5, 7, 11 [P12P8a] and B. and C. pt. 34-1, 2, 3, 5, 6, 7 [P12p8a], A. and B. were incubated at 18°C and C. at 23/28°C. Sr12 confers IT X but there is no ‘typical’ response because of the temperature effects, genetic background effects and interactions. Repeated testing over many years has shown that pt. 34-2, 4, 5, 7, 11 is more avirulent on seedlings with Sr12 than pt. 34-1, 2, 3, 5, 6, 7. The low responses of Thatcher and Celebration are typical of these genotypes. Lee, which shares Sr9g and probably Sr16 with them, is susceptible with both cultures. The low response of Condor with pt. 34-2, 4, 5, 7, 11 is due to both Sr8a and Sr12. in this comparison CS/Marquis 3B appears to be resistant in A. (IT X) but susceptible in B. (IT 3+) reflecting increased virulence of the second pathotype relative to the first. All of these wheats, except perhaps Condor, were susceptible when incubated at 23/28°C.

Use in Agriculture

Sr12 was highly effective against pre-1950 Australian pathotypes. After 1950 the effectiveness of this gene in wheats such as Windebri and Celebration was reduced but not completely overcome. In wheats combining Sr12 with Sr9b or Sr9g the presence of Sr12 can be recognised through its effects on the expression of the Sr9 alleles in seedlings inoculated with avirulent pathotypes. These interactions also appear to occur in adult plants. One pathotype in the University of Sydney collection is known to be unusually virulent on seedlings of Iumillo durum. This culture (pt. 21-7, 9 [71178]) is potentially virulent on wheats known to carry Sr12. Both the seedling and adult plant resistances of Marquillo are more effective than those of Thatcher and its derivatives. The reasons for this are not fully undetstood but Sr12 appears to be involved (RA McIntosh, unpublished 1980; see also Knott, 1984).

In North America Sr12 was very effective in conferring resistance to race 56. Race 15B is virulent.